The present invention relates to a control apparatus of an engine in a vehicle on which an automatic transmission is mounted, more particularly relates to a control apparatus of an engine in which the output characteristic can be changed to a plurality of modes by controlling the air fuel ratio, etc.
To improve the fuel consumption, an engine which can be operated with a higher air fuel ratio than the stoichiometric air fuel ratio has been mounted on the vehicle. In this type of engine, when the air fuel ratio is raised, the output torque is lowered in contrast to a fact that the fuel consumption is improved, and where the engine temperature is low, the combustion becomes difficult to be stabilized, and therefore it is necessary to lower the air fuel ratio, and accordingly the air fuel ratio control has been carried out on a basis of various types of parameters such as a throttle opening degree, engine temperature, etc. One example of an apparatus of performing such a control has been disclosed in Japanese Unexamined Patent Publication No. 60-233332.
Namely, in an engine using the above-mentioned so-called lean burn system, generally, in a state where the throttle opening degree is more than the predetermined level, the air fuel ratio is set on the rich side since the output is regarded as important, and conversely, in a state of a low throttle opening degree, the air fuel ratio is set on the lean side since the fuel consumption is regarded as important. Further, even in a state of the low throttle opening degree, where the engine temperature is low, the air fuel ratio is set be the stoichiometric air fuel ratio or on the rich side so as to stabilize the combustion.
On the other hand, the automatic transmission is constituted so that the motor power transfer route in a gear train, that is the transmission ratio is changed by appropriately engaging or disengaging a frictional engagement device such as a clutch, brake, etc. Accordingly, since these frictional engagement devices transfer the torque or give a reverse force torque, so as to prevent the slippage of the frictional material due to a shortage of the engagement force or an unnecessary consumption of motor power due to an excessive engagement force, the engagement force of the frictional engagement device is controlled in accordance with the torque input from the engine. Concretely, the line hydraulic pressure is controlled so that it becomes a pressure in accordance with the input torque.
As mentioned before, the output characteristic of the engine equipped with the lean burn system becomes a low torque characteristic in a lean burn state where the air fuel ratio is raised, and becomes a high torque characteristic in a state where the air fuel ratio is changed to the stoichiometric air fuel ratio or set on the rich side. The engine equipped with lean burn system provides at least two types of characteristics. The selection of these output characteristics is generally carried out on a basis of the throttle opening degree, and accordingly the output torque in a normal mode is changed as one example as indicated by a fat line in FIG. 10. Nevertheless, since the air fuel ratio is sometimes lowered by the parameters other than the throttle opening degree, for example the engine temperature is low or the like, where for example the engine temperature is low, even if the throttle opening degree is an opening degree TA2 smaller than the predetermined opening degree TA1, the air fuel ratio is lowered and the output characteristic is brought to the high characteristic in some cases. This will be indicated in FIG. 10 as shown by a broken line.
Accordingly, when the throttle opening degree is TA2, two types of engine torques, i.e., an engine torque T1 in a lean burn state and an engine torque T2 with a richer air fuel ratio than this exist. On the other hand, the line hydraulic pressure in the automatic transmission is controlled by the throttle opening degree as one of the parameters, and therefore, in an automatic transmission coupled to the above-described engine in which a plurality of output torques exist with respect to one throttle opening degree, the line hydraulic pressure is controlled in accordance with the high output characteristic. Namely, when the line hydraulic pressure is relatively high with respect to the torque inputted to the automatic transmission, although there is a slight unnecessary consumption of motor power required for generating the high hydraulic pressure, the slippage of the frictional engagement device can be prevented.
In the automatic transmission, however, also the transition state of gear shift is controlled by adjusting the hydraulic pressure, and when that controlled hydraulic pressure is not adequate with respect to the input torque, the gear shift shock is degraded. For example, when the throttle opening degree is a low opening degree in a state where the temperature of the engine is sufficiently high, a lean burn with a raised air fuel ratio is carried out, and therefore the input torque to the automatic transmission becomes low torque, but if the hydraulic pressure of the automatic transmission has been set to a relatively high hydraulic pressure side by expecting the combustion with the stoichiometric air fuel ratio, also an accumulator back pressure controlling the gear shift transition state is shifted with a relatively high pressure. As a result, the torque capacity of the frictional engagement device for an engagement so as to set up a gear shift stage of high speed stage side at an up shift is increased too early period, the gear shift time becomes short, and the gear shift shock is degraded. This state will be indicated as a change in time of the accumulator pressure PACC and the output shaft torque TO of the automatic transmission as shown by a broken line in FIG. 11. Note that, a solid line in FIG. 11 indicates a state where the gear shift shock is good because a pressure adjustment level is adaptable to the input torque.